Long range varifocal optical systems



Oct. 7, 1969 F. G. BACK LONG RANGE VARIFOCAL OPTICAL SYSTEMS Filed Jan. 28, 1965 R O T N E V m United States Patent O 3,471,213 LONG RANGE VARIFOCAL OPTICAL SYSTEMS Frank G. Back, 55 Sea Cliff Ave., Glen Cove, N.Y. 11542 Filed Jan. 28, 1965, Ser. No. 428,760 Int. Cl. G02b 27/32, 7/04, 15/00 U.S. Cl. 350- 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to long range varifocal optical systems and particularly to varifocal optical systems useful in tracking or sighting moving or fixed objects at great distances.

Where it is desired to use varifocal lens systems as part of a sighting or tracking device, it has heretofore been found that there was great loss in pointing accuracy as the reticle normally employed for this purpose shifted with respect to the object when the focal length of the system was changed. This movement of the observed reticle resulted from the necessary play in the movable lens components of the varifocal lens system.

In order to make measurements, using a varifocal lens system for tracking and sighting purposes, it is necessary to know the exact focal length of the said lens system at the time of such measurement. Various devices have been tried for this purpose such as the use of return signals. Such previously tried systems not only proved ineicient but involved large and unwieldy apparatus.

Accordingly, it is an object of the present invention to provide a long range varifocal optical system useful for sighting and tracking distant objects which is free of the limitations of prior art devices.

Another object of the present invention is to provide a long range varifocal optical system having a reticle therein capable of great pointing accuracy despite the movement of the varifocal lens elements.

A further object of the present invention is to provide a calibrated reticle in a long range varifocal optical system, accurate enough for measurements at all times.

Still another object of the present invention is to provide a long range varifocal optical system in which measurements can be read directly without the need for complicated and cumbersome auxiliary devices.

A feature of the present invention is the use of a reticle in the image plane of an objective lens system.

A further feature of the present invention is the use of a varifocal lens system to receive the combined image of the object and the reticle.

Still another feature of the present invention is the use of a calibrated reticle whereby the equivalent focal length of the system can be read directly.

In the accompanying drawing, forming a part hereof there is illustrated one form of embodiment of the in- 3,471,213 Patented Oct. 7, 1969 ICC vention, in which drawing similar reference characters designate corresponding parts and in which:

FIGURE l is a view in longitudinal section of a complete embodiment of the present invention.

FIGURE 2 is a view in front elevation of the reticle image as it appears on the film plane of the invention.

Referring to the drawings and particularly to FIGURE l, 10 indicates a long range varifocal lens system having an objective 11, a collimator '12 and a varifocal lens assembly 13. The objective 11 shown in this embodiment consists of a positive lens system formed of two pairs of air spaced lenses 15, 16, 17, 18.

A reticle 19, is positioned within the lens system 10, at the image plane of the objective 11. The image of the object viewed through the objective 11 and the reticle 19, are thereby superimposed. The collimator 12, which comprises a positive lens system of air spaced lenses 20, 21, 22, 23, receives the light thus transmitted and directs it into the front lens (not shown) of the varifocal lens assembly 13. The varifocal lens assembly 13 thus in effect sees both the object and the reticle 19.

The varifocal lens assembly indicated generally by the block 13 may comprise any mechanically or optically compensated lens system of this type, well known in the art. It is sufficient for the purpose of this invention that the varifocal lens system have the ability, in accordance with well-known varifocal lens operations, to vary the focal length of the system.

The light from the varifocal system 13 is directed onto the film plane of a photographic or television camera, indicated at 14.

It will lbe observed from the foregoing and the following specific example that the objective consists of two groups of air space lenses 15, 16 and 17, 18, having coinciding focal points. The two air spaced positive lens systems 20, 21 and 22, 23, forming the collimator 12 are of shorter focal length and the virtual image of the combined reticle and real image at infinity serve as the object for the varifocal lens system 13. The ratio of the focal length of the front, objective, system 11, to the focal length of the collimator system 12 is the factor by which the different focal lengths of the varifocal lens 13 have to be multiplied to get the equivalent focal length of the combination.

A photographic camera or television camera (not shown) may be positioned to receive the image at the focal plane 14 of the system. The combined image will include the reticle 19 as illustrated in FIGURE 2. It will be observed from an examination of FIGURE 2 that the reticle 19 is provided with calibrations 20 which may be in mils. As the focal length of the system is changed by the operaytion of the varifocal lens system, the calibrations on the reticle 19 will move with the image projected on the focal plane 14. By measuring the movement of one of the calibrations 20, it is possible to read directly the position of the varifocal system in terms of its focal length at any time. Since the reticle 19 is disposed outside of the varifocal lens system 13, it changes its size proportionally to the focal length of the varifocal system. By applying a scale 21, to the calibrated reticle 19, the displacement of any one of the calibrations 20 can be measured. In the case =of a photographic image the `scale can be printed on the film to be viewed. In the case of a television camera the scale can be applied to the viewing screen (not shown) for the purpose of the present invention.

The optical characteristics of a preferred form of long range varifocal optical system according to the present invention is set forth in the following table:

Ivt will be apparent from the foregoing that the varifocal lens system 13 may take various forms, well known EXAMPLE I Radii Thickness (t) Cat. Abbes Lens in mm. Separation (d) Rei. Nd Dispersion No. in mm. No. V

Objective R1= 163.470 15 t;=11.00 BZK-7 1. 51680 64. 1

d1= .100 Ra= -163.470 16 t1=4.500 F-2 1. 6200 36. 34

d2= 1.00 R5= 163.470 17 t3=11.00 13K-7 1. 51680 64. 19

d3: .100 R1= -163.470 18 t4=4.500 F-2 1. 6200 36. 34

d4= 171. 590 EFL: +1886 mm. (+5802 Dio eters) Reticle (15:49.29 Collimator:

Rn=403.740 20 t f,=2.000 SF-IZ 1. 64830 33. 76

do= .100 Ru= 54.980 21 t=6.000 BK-7 1. 51680 64. 19

d1=6.20 R13=403.74O 22 t1= 2.000 SF-12 1. 64830 38. 76

da: .100 R15= 54.980 23 ts= 6.000 BK-7 1. 51680 64. 19

dg: 5.000 EFL= +60.796 mm. (+16.448 Diopters) B K: Borosiicate Crown.

SF: Dense Flint. Fn Flint.

Nd is the index of retraction for d light.

The optical characteristics of a second preferred form of a long range varifocal optical system according to the in the art, and be either of the optically compensated type, as illustrated, or mechanically compensated.

present invennon 1s set forth 1n the following table: 40 F rom the foregoin g 1t will be observed that there has EXAMPLE II Thickness (t) Glass Index Abbes Lens Radii Separation (d) Cat. Nd Dispersion No. in mm. in mm. Ref. No. V

Objective:

Rx= 163.470 15. t1=11.00 13K-7 1. 51680 64. 19

d1= .100 R3 163.470 16 i2=4.500 1"-2 1. 6200 36. 34

dg: 1.00 R= 163.470 17 t3= 11.00 13K-7 1. 51680 64. 19

d3= .100 R1= 163.470 18 !4=4.500 F-Z l. 6200 36. 34

d4= 171.590 EFL= +188.60 mm. (+6302 Dio eters) Reticle.

d5= 49.89 Collimator:

Ru=356.990 20 t5=2.000 SF 12 1. 64830 33. 76

d=2.00 R11=57.390 21 iu=7.000 13K-7 1. 51680 64. 10

d1=4.800 R13= 127.580 22 1=2.000 SF-12 1. 64830 33. 76

d3= .200 R15= 44.510 23- ta=7.000 13K-7 1. 51680 64. 19

dn: 5.000 EFL= +60.805 mm. (+16.446 Diopters) BK=Borosi1icate Crown.

SF=Dense Flint. F-Flin been provided a long range varifocal optical system particularly adapted for use as part of a sighting or tracking device which will have high pointing accuracy and also Iprovide a -ready means for determining the exact focal length of the lens system at any given time.

Having thus fully described the invention, what is tive to receive the light from the image generated by the objective and passing through the reticle and form a superimposed virtual image of the object and the recticle, a. varifocal lens system to receive the light coming from the collimator, in which `the lenses have the following optical characteristics:

Lens Radii Thickness (t) Cat. Abbes No. in mm. Separation (d) Ref. Nd Dispersion in mm. N o. V

Objective:

R1=103.470 15. 1=11.00 BK-7 1. 51680 64. 1

R2;- -1e3.47o

d1=.100 Ra= 163.470 16 tz=4500 F-2 1. 6200 36. 34

dz= 1.00 R5= 163.470 17 3=11.00 BK7 1. 51680 64. 19

d3= .100 R7= -163.470 18- t4=4.500 yF-Z 1. 6200 36. 34

d4= 171. 590 EFL=+188.6 mm. (+5.302 Dio Jters) Reticle iF-19.29 Collimator;

Rg=403.740 20 t5= 2.000 SF-12 1. 64830 33. 76

da= .100 Ri1== 54.980 21 125:6.000 BK-7 1. 51680 64. 19

d1: 6.20 Ri3=403.740 22- t1= 2.000 SF-12 1. 64830 38. 76

ds= .100 R= 54.980 23 ta=6.000 BIC-7 1. 51680 64. 19

dg=5.000 EFL=+60.796 mm. (446.448 Diopters) BK=Borosilicate Crown. SF=Dense Flint.

F= Flint.

Nd is the index of refraction for d light, and means to vary the focal length oi the varlx'ocal lens system and direct an image ofthe object and the reticle upon a focal plane.

claimed as new and desired to be secured by Letters Patent of the United States, is:

1. A long range varifocal lens system comprising-an objective to receive light from an object, a reticle disposed in the image plane of the objective, a oolli-mator having a 2. A long range varifocal lens system comprising an objective to receive ligh-t from lan object, a reticle disposed in the image plane of the objective, a collimator having a focal plane coincident with the image plane of the objectiv to receive the light from the image generated by focal plane coincident with the image plane of the objecthe objective `and passing through the reticle and form la superimposed virtual image of the object and the reticle, a.

collimator, in which the lenses have the following optical dg=5.000 EFL=+60.805 mm. (+16.446 Diopters) varifocal lens system to recelve the light coming from the characteristics:

Lens Radii Thickness (t) Glass Index Abbe's No. in mm. Separation (d) Cat. Nd Dispersion in mm. Ref. No. V

Objective R1=163.470 16 t1=11.00 :BK-7 1. 51680 64. 19

d1=.100 Rz= 163A70 16 ta=4.500 F-Z 1. 6200 38. 34

dg= 1.00 R5= 163.470 17 t3=11.00 :BK-7 1. 61680 64.19

dg: .100 R1= -163.470 18 l4=4.500 F-Z 1. 6200 36. 34

R.=4,1s5.1o0

d4= 171.590 EFL= +188.60 mm. (+5.302 Dio pters) Reticle d5=49.89 Cellimator:

Rn: 356.990 20 i5=2.000 SF-12 1. 64830 33.76

d|=2.00 Rn=57.390 21- t5=7.000 BK-7 1. 51680 64. 19

d1=4.800 Rn= 127.580 22 t1=2.000 SF-12 1. 64830 33. 70

d= .200 R15=44.510 23 t5=7.000 13K-7 1. 51680 64. 19

BK=Borosilicate Crown.

SF=Dense Flint.

F int. Nd is the index of retraction for lens system and direct an image References Cited UNITED STATES PATENTS 6/1968 Burrig et al 350-10 X DAVID SCHONBERG, Primary Examiner T. H. KUSMER, Assistant Examiner d light, and means to vary the focal length oi the variiocl of the object and the reticle upon a focal plane. 

